One of the most critical aspects of the operation of railroad vehicles is the predictable and successful operation of the air brake system. However the air brake system is subjected to a variety of dynamic effects, not only as a result of the controlled application and release of the brakes through changes in brake pipe pressure, but also due to varying operating conditions encountered by the train. Thus multiple operating scenarios must be considered for the successful design and operation of the air brake system.
At each railcar, a control valve (typically comprising a plurality of valves and interconnecting piping) responds to operator-initiated changes in the brake pipe fluid pressure by applying the brakes (in response to a decrease in the brake pipe fluid pressure) or by releasing the brakes (in response to an increase in the brake pipe fluid pressure). The fluid within the brake pipe conventionally comprises pressurized air. The control valve at each rail car senses the drop in brake pipe air pressure as the pressure drop propagates along the brake pipe. In response, at each railcar pressurized air is supplied from a local rail car reservoir to the wheel brake cylinders, which in turn drive the brake shoes against the railcar wheels. The railcar reservoir is charged by taking air from the brake pipe during non-braking intervals. Typically, the pressure reduction in the brake pipe for signaling a brake application is about seven to twenty-four psi, with a nominal steady state pressure of about 90 psi. The braking pressure applied to the railcar wheels is proportional to the drop in the brake pipe pressure. Thus it can be seen that the brake pipe serves to both supply pressurized air to each railcar for powering the brake shoes during a brake application and also serves as the medium for communicating brake application and release instructions to each railcar.
The railcar brakes are applied in two different modes, i.e., a service brake application or an emergency brake application. A service brake application involves the application of reduced braking forces to the railcar to slow the train or bring it to a stop at a forward location along the track. During these brake applications the brake pipe pressure is slowly reduced and the brakes are applied gradually in response thereto. An emergency brake application commands an immediate evacuation or venting of the brake pipe and in response an immediate application of the railcar brakes. Unfortunately, because the brake pipe runs for several thousand yards along the length of the train, the emergency braking evacuation does not occur instantaneously along the entire length of the brake pipe. Thus the braking forces are not uniformly applied at each railcar to stop the train.
After an emergency brake application, or two or three service brake applications, the brake pipe must be recharged to its nominal operating pressure by supplying pressurized air from a reservoir on the locomotive into the brake pipe. Effective subsequent brake applications cannot be made until the recharging process has been completed.
FIG. 1 illustrates a typical prior art brake system employed by a railway freight train. In a conventional train having only a lead locomotive, the train brake system comprises a locomotive brake system located on a locomotive 100 and a set of car brake systems located on a set of railway cars illustrated by a railcar 200. The application and release of braking action is controlled by an operator within the locomotive 100 using a manually operated brake handle. The locomotive includes an air brake control system 102, for supplying air pressure to or venting a controllably pressurized brake pipe 101 via a brake pipe valve 120. The pressurized brake pipe 101 is in fluid communication with each of the railcars 200 of the train as shown.
The locomotive brake control system 102 comprises an art supply input link 111 for supplying pressurized fluid (air) through which the brake pipe 101 is charged. A flow measuring adapter 113 is connected to the air supply link 111 for measuring the charging rate (as a differential pressure) of the brake control system 102. An output terminal 116 of the flow measuring adapter 113 is connected to an input port 121 of a relay valve 117. A bi-directional port 122 of the relay valve 117 is coupled to the brake pipe 101. The relay valve 117 further includes a port 123 coupled through an air pressure control link 103 to an equalizing reservoir 105. The pressure control link 103 is also connected to a pressure control valve 107 through which the equalizing reservoir 105 is charged and discharged in the process of a brake operation. A port 124 of the relay valve 117 is controllably vented to the atmosphere as an exhaust port. Coupled with brake pipe 101 and air pressure control link 103 are respective pressure measuring and display devices 131 and 133. The brake pipe gauge 131 measures the air pressure in the brake pipe 101 and the equalizing reservoir gauge 133 measures the pressure in the equalizing reservoir 105.
The components of a railcar air brake control system 202, include a control valve 203 having a port 221 coupled to the brake pipe 101. The control valve 203 also includes a port 222 coupled to a pressure storage and reference reservoir 205. Finally, the control valve 203 includes a port 223 coupled to an air brake cylinder 231, comprising a piston 232 connected to a brake shoe 233. An increase in air pressure at the port 223 is fluidly communicated to the piston 232 for driving the brake shoe 233 against the wheels 235 of the railcar 200. Thus the air brake control system 102 of the locomotive 100 controls operation of the pneumatically operated brake shoes 233 at each of the wheels 235 of each railcar 200.
During train operation, the brake pipe valve 120, through which the components of the brake control system 102 are coupled to the brake pipe 101, is open to create a continuous brake pipe fluid path between the locomotive 100 and all of the railcars 200 of the train. The brake pipe valve 120 is controlled by a brake valve cut-out valve 250, that is in turn controlled by a pilot valve 251. The pilot valve 251 is manually operated by the locomotive operator to close the brake pipe valve 120 when it is desired to terminate brake pipe charging or to disconnect the brake pipe 101 from the locomotive brake control system 102. There are also other valves (not shown in FIG. 1) that automatically terminate brake pipe charging during an emergency brake application by closing the brake pipe valve 120. Each railcar 200 also includes a manually-operated brake pipe valve 240.
The brake system is initially pressurized by the operation of the pressure control valve 107, which controls the air supply to the line 103 to charge the equalizing reservoir 105 to the predetermined pressure. The relay valve 117 is then operated to couple port 121 with port 122 so that air is supplied there through to the brake pipe 101, charging the brake pipe 101 to the predetermined charged pressure, as established by the pressure of the equalizing reservoir 105. When the brake pipe pressure reaches the predetermined pressure, the pressure at the port 122 (connected to the brake pipe 101) equals the pressure at port 123 (connected to the equalizing reservoir 105). At this point the brake pipe is charged and the fluid flow path from the equalizing reservoir 105 to the brake pipe 101 via the relay valve 117 is closed.
The pressure storage and reference reservoir 205 of each railcar 200 is fully charged from the brake pipe 101 through the control valve 203, thereby establishing a reference pressure for maximum withdrawal of the piston 232 and complete release of the brakes 233 for each of the cars 200.
To brake the railcars 200, the train operator operates the pressure control valve 107 using the braking handle. This operation causes a partial venting of the air pressure control link 103 through the exhaust port of the pressure control valve 107, reducing the pressure within the equalizing reservoir 105. This pressure reduction is sensed by the relay valve 117 at the port 123. In turn, the pressure reduction causes the bi-directional port 122 to be coupled to the exhaust port 124, thereby exhausting the brake pipe 101 to the atmosphere. The venting of the brake pipe 101 continues until the pressure within the brake pipe 101 equals the pressure of equalizing reservoir 105.
As the pressure in the brake pipe 101 falls, the control valve 203 in each of the cars 200 senses the pressure reduction by comparing the brake pipe pressure with the pressure of the pressure storage and reference reservoir 205. This pressure reduction causes a corresponding increase in the air pressure applied to the brake cylinder 231 from the port 223, resulting in an application of the brake shoes 233 against the wheels 235 in proportion to the sensed pressure reduction in the brake pipe 101.
Further pressure reductions in the equalizing reservoir 105 by the train operator produce corresponding pressure reductions in the brake pipe 101 and, corresponding additional braking effort by the brake shoes 233 in each of the railcars 200. In summary, the intended operation of the brake system in the cars 200 and specifically the braking effort applied in each of the cars 200, is proportional to the reduction in pressure in the equalizing reservoir 105 within the locomotive 100.
When the locomotive operator desires to release the train car brakes, she operates the pressure control valve 107 to effectuate a recharging of the air brake system 102. The recharging is accomplished by bringing the pressure within the equalizing reservoir 105 back to its fully charged state by supplying pressurized air via the flow measuring adapter 113 and the relay valve 117. With the equalizing reservoir 105 recharged, there is again a pressure differential (but opposite in sign to the previous pressure drop in the pressure line 103) between the ports 122 and 123 of the relay valve 117 that causes the brake pipe 101 to be charged with pressurized air from the equalizing reservoir 105. The brake pipe pressure increase is sensed by the control valve 203 in each of the railcars 200 to cause the brake shoes 233 to be released by the action of the brake cylinder 231.
Distributed power train operation supplies motive power from a lead locomotive and one or more remote locomotives spaced apart from the lead unit in the train consist. Distributed train operation may be preferable for long train consists to improve train handling and performance. Each lead and remote locomotive includes an air brake control system, such as the air brake control system 102 discussed above, and a communications system for exchanging information between the lead and remote units. Conventionally the communications system comprises a radio frequency link and the necessary receiving and transmitting equipment at each of the lead and remote units.
The description of the present invention below with respect to the brake control system of a remote locomotive in a distributed power train consist refers to the same brake control system components and uses the same reference characters as described above in conjunction with the brake control system of the lead locomotive. Specific mention will be made if the reference pertains only to the lead or only to the remote locomotive.
On distributed power trains equipped with UIC (Union Internationale de Chemins Fer) wagon braking equipment, braking is accomplished by venting the brake pipe 101 at both the lead and remote locomotives, thus accelerating the brake pipe venting and the application of the brakes at each railcar, especially those railcars near the end of the train. Brake pipe venting at only the lead unit requires that the brake pipe pressure reduction propagate the length of the train, thus slowing brake applications at railcars distant from the lead unit. For a distributed power train with an operative communications link between the lead and remote units, when the train operator commands a brake application by operation of the brake handle at the lead unit, a brake application command is transmitted to each remote unit over the radio frequency communications link. In response, each remote unit also vents the brake pipe through its respective pressure control valve 107. A brake release initiated at the lead unit is also communicated over the radio frequency link to the remote units so that the brake pipe 101 is recharged from all locomotives. Thus braking actions at the remote locomotives follow the braking actions of the lead unit in response to signals transmitted by the communications system.
If the communications system is inoperative or if the communications link between the lead unit and the remote units is disrupted (for example, if line-of-sight directivity is lost due to track topology or an interfering object), when the lead operator makes a brake application the remote locomotives will not receive the brake application command via the communications system. Thus the brake application is executed by venting the brake pipe only at the lead locomotive, resulting in a slower brake application at all the railcars.
It is known that leaks develop in the brake pipe and thus in one operational mode for a distributed power train the remote units (and the lead unit) continually charge the brake pipe 101 when the pressure falls below a nominal value. The remote units sense the brake pipe pressure via the relay valve 117 by comparing the equalizing reservoir pressure with the brake pipe pressure. Whenever the brake pipe pressure is less than the equalizing reservoir pressure, the brake pipe 101 is charged from the air supply 111 via the relay valve 117.
A dangerous scenario can develop if a brake application command transmitted from the lead unit does not reach the remote locomotive while the latter is monitoring and recharging the brake pipe whenever the pressure drops below the nominal predetermined value. In this situation the remote locomotive continues to recharge the brake pipe 101 as the lead unit is venting the brake pipe to signal a brake application to the railcars 200. This situation can cause dangerously high in-train forces to develop.
One prior art technique for avoiding this scenario is to automatically close the brake valve 120 of the remote unit whenever communications is lost between the lead and the remote locomotive units. With the brake valve 120 closed, the remote units cannot recharge and cannot vent the brake pipe 101. Thus all brake signaling (both brake applications and brake releases) over the brake pipe 101 is initiated from the lead unit. Although under these conditions the remote locomotives cannot assist with the brake pipe venting to accelerate brake applications, the remote locomotives also cannot erroneously recharge the brake pipe while the lead unit is venting it.
The prior art LOCOTROL® distributed power communications system (available from the General Electric Company of Schenectady, N.Y.) incorporates a variant of the technique described above by including a brake pipe flow sensing function at each remote locomotive unit in a distributed power train. A flow sensor, such as an airflow detector 252 depicted in FIG. 1, is included in the brake pipe path at each remote unit to detect a declining brake pipe pressure (representing a brake application command). If the rate of decline exceeds a predetermined value a brake application is declared. If the communications system is also concurrently inoperative, then in response to simultaneous occurrence of these two events, the remote unit brake valve 120 is commanded to a cut-out or closed position. Proper execution of the command closes the remote unit brake valve 120. The brake application initiated by the venting of the brake pipe at the lead unit cannot be countered by pressurizing of the brake pipe at the remote unit.
If the command to cut-out or close the brake valve 120 is not properly executed, then the brake valve at the remote unit remains open. There are several possible causes for this scenario, including a failure of the brake valve cut-out valve (i.e., the valve that drives the brake pipe valve into a cut-off or closed configuration), a failure of the pilot valve that drives the brake valve cut-out valve, or a brake pipe valve stuck in the open position. Thus, if the brake valve is not closed or cut-out as commanded, and during a communications system failure the lead unit issues a brake application, then the remote units continue to supply brake pipe recharging pressure while the lead unit is venting the brake pipe to apply the railcar brakes. This sets up an undesirable situation where the front railcars experience maximum braking and rear railcars experience minimum or no braking action. The net result is that the rear of the train can run into the front of the train, causing high in-train forces and possible derailment.